+1 for air suspension, but look at your cheaper options first IMO.
Back of my ute is On-Air replacement c/-previous owner, so can't comment on difficulty of install.
On the rare occasions passengers are in the back off-road, feedback has been positive about ride quality! Ride has been worse in cab on the springs.
If you're looking at going down the air path, budget for an on board compressor + controllers too, as adjusting bag pressure via tyre-type valves is annoying.